1. Field of the Invention.
A printed-circuit disc is used to interconnect a seismic detector, such as a geophone, with at least one seismic cable.
2. Description of the Prior Art.
In seismic prospecting, whether on dry lands or marsh and swamp areas, "spread" cables are used to interconnect "strings" of geophones to seismic recording instruments. Each string connects two or more geophones having electric junctions along the geophone "leader" wires which are connected to a pair of conductor wires in the spread cable. The geophone casing is implanted into the earth to allow the geophone to detect returned seismic waves.
In practice, the geophones are electrically interconnected into the leader wire at spaced intervals in various networks consisting of series and parallel combinations. The process of interconnecting geophones is commonly referred to as "stringing". The art of geophone stringing has been plagued with numerous problems which are described, for example, in U.S. Pat. Nos. 3,119,978, 3,445,809, 3,930,218, 3,956,575, 3,993,859 and 4,122,433.
As will be appreciated from a detailed study of these patents, the art of connecting geophone terminals to leader cables, of stringing geophones into series and parallel combinations from which cable spreads are formed, and of anchoring geophone leader wire to geophone casings, requires considerable skill and time, both in making the initial assemblies and subsequently in disassembling certain ones of the geophones which require repair. Some repair jobs in the field require special purpose tools which are not generally available in remote areas, as in jungles or swamps.
In certain ones of the prior art methods, T-type couplers are used for joining leader cables. One type of commercially known T-coupler is a completely molded T around the cable's junction thereby providing no access to the electric conductor wires; another type is a fastened T formed from two members which are clamped together around the junction, and then the inside of the T is filled with a suitable potting compound. Both known T-couplers provide a waterproof junction, but the molded T is impossible to repair in the field because the seismic crew has no injection molding equipment, while the fastened T requires considerable skill and time to first dismantle and remove the potting compound and then to reassemble and to reshoot the compound into the T.
Another type coupler for joining three cables is disclosed in said U.S. Pat. No. 3,956,575 which requires no potting compounds, but in this patent, the leader cable is connected to the geophone casing in a conventional manner. This method is still labor-intensive and is prone to human error. Such errors are normally not detected until final checkout is made on the assembled geophone strings and cable spreads. When a defective geophone string is found it is very time-consuming to locate the origin of the trouble which frequently lies in erroneous inter-wire connections.
In addition to the problems encountered while stringing the geophones in the place of manufacture of the geophones and geophone strings, problems also exist in the field use of geophone strings. Thus, cables, couplers, and geophone casings become frequently damaged by physical objects and their outer jackets and housings are eaten up by rodents, or they become damaged by rough handling. If trouble shooting is very time-consuming or costly, sometimes a very expensive entire geophone string may have to be discarded because the fault cannot be easily located.
It is a main object of the present invention to overcome the above-mentioned drawbacks of the known geophone stringing art and to provide a method and means for stringing geophones which allows ready access to and easy recognition of the junctions between geophone leader wires and geophone terminals. The invention reduces considerably the amount of labor required in preparing leader cables, in making connections between the geophone terminals and the leader wires, and in anchoring the leader wires to the geophone casing.
It is a further object of the present invention to reduce, as much as possible, the possibility of human error in the assembly, and the subsequent trouble shooting of the geophone strings, which are, therefore, superior from the standpoint of both cost and reliability.